1. Field of the Invention
The present invention relates to a structure for dealing with impurities contained in recycled toner and more particularly to a developing device configured to obviate defective images ascribable to the impurities and an image forming apparatus including the same.
2. Description of the Background Art
It is a common practice with a copier, facsimile apparatus, printer or similar image forming apparatus to develop a latent image formed on a photoconductive element or image carrier with toner, which is contained in a developer. Developers are generally classified into a single-component type developer, i.e., magnetic or nonmagnetic toner and a two-ingredient type developer made up of a magnetic carrier and toner deposited on the carrier. The toner contains a pigment therein. The two-ingredient type developer is deposited on a sleeve, which accommodates a magnet roller therein, in the form of a magnet brush and brought into contact with a latent image formed on the photoconductive element. When the magnet brush contacts the latent image, the toner is caused to deposit on the latent image for thereby producing a corresponding toner image.
To maintain the toner content of the developer constant, fresh toner is replenished to make up for the consumption of the toner ascribable to repeated development. However, if only fresh toner is repeatedly replenished, used toner is often simply discarded. It has recently been proposed to return residual toner removed from the photoconductive element after image transfer to the developing device, thereby recycling the toner. This not only reduces loads on environment, but also enhances yield. Such recycled toner, however, has the following problems left unsolved.
The recycled toner differs from fresh toner in that it contains impurities including paper dust derived from sheets to which toner images are transferred. Paper dust is scraped off the photoconductive element together with the toner after image transfer and then returned to the developing device together with the toner. Paper dust not only obstructs the deposition of the toner on a latent image, but also effects the charging characteristic of the toner. Further, when the paper dust enters the developing device, it often degrades the fluidity of the toner being agitated in the developing device, preventing the toner from achieving an expected charging characteristic.
Moreover, assume that the developer containing the recycled toner and paper dust together with fresh toner moves away from a doctor blade or regulating member. Then, the paper dust deposits on the background area (white portion) of the photoconductive element when the developer contacts the latent image. This results in the local omission of a toner image and defective charging, which is ascribable to the deposition on the background area. More specifically, when a charger is used, the paper dust obstructs the injection of charge into the portion where it has deposited.
Why the recycled toner and paper dust deposit on the background of the photoconductive element will be described hereinafter. The residual toner and paper dust collected from the photoconductive element are lower in charging ratio than fresh toner even when returned to and agitated in the developing device. Therefore, the electric coupling force of the residual toner and paper dust with the carrier is weak and unstable, so that such toner and paper dust leave the carrier during rotation of the sleeve due to a centrifugal force and an air stream. The recycled toner and paper dust so released from the carrier fly around the sleeve and photoconductive element or deposit on surrounding members. Consequently, the recycled toner and paper dust contaminate the background area of the photoconductive element when deposited there.
In light of the above, Japanese Patent Laid-Open Publication Nos. 10-260583 and 11-311902, for example, disclose classifying means including a mesh filter. The classifying means, however, not only makes the construction sophisticated, but also increases the cost because a measure against the stop-up of the mesh filter is necessary. Furthermore, impurities removed by the mesh filter constitute another matter that must be discarded. While a special construction using a bias for the collection of impurities may be contemplated, it also increases the cost.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 5-72886 and 11-327289.
It is an object of the present invention to provide a structure for dealing with impurities contained in recycled toner.
It is another object of the present invention to provide a developing device capable of obviating defective images ascribable to impurities, which are contained in recycled toner, and an image forming apparatus including the same.
A developing device for feeding a developer stored therein to an image carrier of the present invention includes a sleeve facing the image carrier for causing the developer deposited thereon to contact a latent image formed on the image carrier. A regulating member faces the sleeve for regulating the thickness of the developer that forms a layer on the sleeve. A guide member has a guide surface for guiding the developer regulated by the regulating member toward the surface of the image carrier. The guide surface has a conductive surface facing the sleeve.
An image forming apparatus including the above developing device is also disclosed.